1. Field of the Invention
This invention relates to a photoelectric conversion module and, in particular, a photoelectric conversion module adapted for multiple channels.
2. Description of the Related Art
Recently, in accordance with speeding up of communications, a high-speed transmission I/O interface (I/O architecture) such as InfiniBand and PCI Express (which are registered trademarks in USA) is put to practical use. The high-speed transmission I/O interface (I/O architecture) can provide a high-speed by bundling multiple channels.
In general, a photoelectric conversion module used for the I/O interface is constructed such that an optical transmission assembly (or transmission side photoelectric conversion part) and an optical reception assembly (or reception side photoelectric conversion part) are mounted on one circuit board (See, e.g., JP-A-2008-90232).
The photoelectric conversion module includes a card edge connector that a connecting terminal is formed at one end of a circuit board for electrical connection to an information system device to be connected therethrough, where the card edge connector is fitted to a card edge socket on the information system device.
However, in the conventional photoelectric conversion module, the connecting terminals for transmission and reception need to be formed at one end of one circuit board since the transmission side photoelectric conversion part and the reception side photoelectric conversion part are mounted on the one circuit board. As the number of the channels increases, the number of connecting terminals increases to widen the width of the card edge connector. There occurs the problem that the size of the card edge connector increases.
For example, a photoelectric conversion module adapted for 12-channel bidirectional communications (12 channels for transmission and 12 channels for reception) needs 48 connecting terminals for transmission and reception since two connecting terminals are needed for each one channel to allow transmission with differential electrical signal. In this case, the card edge connector of the conventional photoelectric conversion module needs at least a width for 24 connecting terminals even when the connecting terminals are formed on both sides of the circuit board. Therefore, the width of the card edge connector increases such that the photoelectric conversion module becomes larger.
In order to decrease the width of the card edge connector, a construction may be made that two circuit boards of a transmission side circuit board and a reception side circuit board are used to form a double card edge connector by mounting the connecting terminals on the respective circuit boards.
In accordance with the I/O interface standards, the double card edge connectors for transmission and reception need to have a predetermined clearance to match the dimensions of an edge connector socket to be connected. Furthermore, the entire photoelectric conversion module needs to have predetermined dimensions in vertical and horizontal widths.
In such a construction, it becomes difficult to efficiently dissipate heat generated at the transmission side photoelectric conversion part on the transmission side circuit board and at the reception side photoelectric conversion part on the reception side circuit board during the operation of the photoelectric conversion module.